 Cytotoxicity

Cytotoxicity is the capacity of an exposure or agent to damage or kill biological cells. Its measurement depends on the cell type, exposure conditions, observation time and endpoint. A test of cell viability, membrane damage or metabolic activity records a particular response; it does not by itself identify every mechanism of injury or establish overall biocompatibility.

A motivating experiment is T. Mosmann's 1983 tetrazolium salt colorimetric assay. Living mammalian cells produced a measurable signal read with a multiwell scanning spectrophotometer. The primary paper explicitly notes that the signal depends on cellular activation, permitting studies of survival, proliferation and activation.^[ref]

For an original blank-corrected comparison, suppose the treated culture gives absorbance $A_t=0.45$, the matched control $A_c=0.85$ and the reagent blank $A_b=0.05$. The relative assay signal isCalling this a relative signal states exactly what was calculated. It does not establish that half the cells died. In a linear response model $A-A_b=qN$, either halving viable-cell number $N$ at fixed per-cell response $q$, or halving $q$ with no change in $N$, produces the same result.

A useful experiment therefore compares complementary endpoints and controls for the exposure vehicle, reagent background and direct optical interference. A material-only blank can reveal color or light scattering from the tested substance itself. Independent cell counts or a membrane-integrity measurement address different ambiguities from repeated readings of the same optical signal. Reduced proliferation and cell death should be distinguished when interpreting an apparent cytotoxic response.